Field of the Invention
The present invention relates to a valve, system and method for completion, stimulation and subsequent re-stimulation of well(s) or borehole(s) for hydrocarbon production.
Related and Prior Art
The process of making a production well, after drilling it, ready for production and/or injection is called completion of a well. This principally involves preparing the bottom of the borehole at or in the proximity of the production layer(s) to the required specifications, running in the production tubing or pipe and its associated downhole tools, as well as perforating and stimulating, as required. The process of running in and cementing the casing can also be included, if necessary due to the strata structure. All these processes will be described in detail below.
A subterranean formation containing hydrocarbons consists of at least one layer of soft or fractured rock(s) or strata containing the hydrocarbons, in the following called a production layer. Each production layer must be covered by a layer of impermeable rock(s) or strata preventing the hydrocarbons from escaping. The production layers in an oil or gas field are collectively known as a reservoir.
The drilling can be done vertically through one or more strata/rock layers in order to reach the desired production layer(s), and then possibly horizontally along one or more strata to provide as efficient well(s) as possible. A production well extending through the reservoir is conventionally divided into production zones, and particularly one or more production zones per production layer. A production well may extend several thousand meters vertically through the formation, and be connected to substantially horizontal branches extending up to several kilometers through the production layer(s).
The drilling in the geological strata can be done by rotating a drill bit at the end of a drill string and forcing it in the desired direction through geological or rock layers or strata to create or form a wellbore. Once a predetermined length of the wellbore is drilled, the drill string with the drill bit may be pulled out, and the wellbore may be lined with a steel pipe called a casing or liner. Hence, an outer annular space is formed between the casing and the formation. It is a common, but not obligatory, practice to cement the casing to the formation by filling all or part of the outer annular space with cementing slurry or slurries. Open boreholes or wellbores are also common, when the strata allow having such. A fully or partially cemented casing can stabilize the formation, and at the same time can make it possible to isolate certain layers or regions behind the casing for retrieval of hydrocarbons, gas, water or even geothermal heat. It is well known to anyone skilled in the art that e.g. epoxy/resin-based cementing slurries in some cases are better suited for the task than cement based mixtures. The terms “cement” and “cementing” are thus to be construed generally as use or injection of a viscous slurry, which then hardens, for the purpose of retaining the casing in the formation and/or stabilizing the formation and/or creating a barrier between different zones, and not exclusively as use of cement only. Cementing tools or valves may be arranged in the casing at predetermined locations. When a segment of the casing is to be cemented, the cementing valve is opened and cement slurry is pumped down the casing, out through the valve-ports, and into the outer annular space between the casing and the formation. The person skilled in the art will be familiar with the use of suitable plugs, staged cementing, in which a first batch of cement or liquid slurry is allowed to set before the next batch of cement or liquid slurry is pumped into the outer annular space above it, thus reducing the hydro-static pressure from the cement, which might otherwise harm or damage a weak formation, and other cementing techniques and details.
During cementing, injection and production in wells as those described above, the possibility for large differential pressures between different zones increases with increasing depth(s). Production of hydrocarbons from strata deep below the seabed and geothermal applications are both likely to involve large or high pressures. Isolation of zones and injection of liquid or gas to increase the pressure in the production zones or regions can lead to correspondingly large differential pressures.
When a well is drilled and lined with a casing, a return flow path from the formation around the casing to the surface must be established. In some instances, it is possible to penetrate the casing by setting off explosive charges at one or more predetermined depths to enable radial flow of production fluid from the formation into the casing. In other instances, the casing may be provided with prefabricated holes or slits, possibly combined with sand screens. In many applications, the combination of high hydraulic pressure and relatively porous production strata implies a substantial risk for damage of the formation if explosives are used to penetrate the casing. In these cases, it is a common practice to use valve sections with radially extending openings which are opened to allow radial flow of cement or epoxy/resin out of the casing for stabilizing and retaining the casing in the formation, for radial flow of injection fluid from inside the pipe to the surrounding formation to maintain or increase the hydraulic pressure in the formation, and/or for radial flow of production fluid from the formation into the casing. Such valve sections designed for inclusion in a tubular, usually by means of threaded couplings of the same kind as used when connecting the pipe segments to a string, are called “valves” in the following for simplicity.
Hydraulic fracturing, poses particularly demanding requirements to the design, robustness and durability of the valve(s). In hydraulic fracturing, a mixture containing e.g. 4% small ceramic particles can be injected into the formation at a pressure quite above the formation pressure. Fractures in the formation are expanded by the pressure and filled with these particles. When the hydraulic pressure is removed, the particles remain in the fractures and keep them open. The purpose is to improve the inflow of production fluid from the formation.
It is also a common practice to insert at least one production pipe into the casing. The inner annular space between the casing and the production pipe is filled with a suitable liquid/fluid or mud, and is generally used to maintain and increase hydraulic pressure. The production pipe is in these cases used as the return path, and conveys the production fluid up to the surface. When using a production pipe within the casing, it is of course also necessary to provide the production pipe with openings or apertures for production fluid, and it may be necessary to isolate production zones from the liquid/fluid or mud in the inner annular space between the production pipe(s) and the casing. Isolating the different zones can be accomplished by using mechanical plugs called “packers”, rather than by using cementing slurry or slurries. Such packers are mainly used in the inner annular space between the production pipe and the casing, because it may be problematic to achieve sufficient sealing against the formation, especially if the formation is porous. Valves corresponding to the valves described above can be arranged in the production pipe(s), and they can be opened once they are localized in the production zone(s).
One or more injection wells may be provided at a distance from the production well(s) in a field. The injection well(s) can be used to pump water, saline or gas back into the formation in order to increase the pressure. Additives such as acid, solvents or surfactants may be added to the fluid in order to enhance production of hydrocarbons in processes known as “stimulating a zone”.
Valves can be used to control the flow of formation fluid from a production zone into the production pipe through the casing, possibly through a horizontal and/or vertical branch. Valves can also be used for controlling an injection fluid from an injection well into a certain zone of the formation to be stimulated. When the formation fluid from a production zone contains too much water to be economically sustainable, the production zone can be shut down, typically by means of one or more valves. The valves are operated between open and closed, and possibly choked, positions using a variety of techniques, including use of wireline tools, strings of pipes, coiled tubing, self-propagating tools known as borehole or well tractors or runners, and drop balls. Some valves may be operated using separate hydraulic control lines. However, the space and cost required for providing separate hydraulic control lines and relatively expensive hydraulic valves quickly make hydraulically operated valves impractical for use in a tubular with many valves.
Hence, it is an object of the present invention to provide a tubular or a pipeline with a large number of valves, while avoiding expensive valves, hydraulic control lines and/or unnecessary loss of expensive production time, etc.